1. Field of the Invention
The present invention relates generally to a stepping motor and a driving apparatus and, more particularly, to a stepping motor provided with exciting coils and a rotor provided with N/S poles so as to rotate following an excitation state of the exciting coils and also to a driving apparatus to drive a driven member by means of rotation of the stepping motor.
2. Description of the Related Art
An indicating apparatus, wherein a pointer for indicating, for example, a speed of a vehicle or a rotation speed of an engine is a driven member, is conventionally known as a driving apparatus having a stepping motor. The above indicating apparatus, as shown in FIG. 5, has a stepping motor 1 having exciting coils 1a1, 1a2 and a rotor 1b on which five sets of N/S poles are magnetized in turn and which rotates following a change of an excitation state of the exciting coils 1a1, 1a2, a pointer 2 being linked with the rotational drive of the rotor 1b, a gear 3 to transmit the rotational drive of the rotor 1b to the pointer 2, and a drive controller 4 to rotate the rotor 1b normally or reversely by controlling the excitation state of the exciting coils 1a1, 1a2.
Hereinafter, a relation between an excitation state of the exciting coils 1a1, 1a2 and rotation of the rotor 1b is described with reference to FIGS. 6A-6H. First, in an excitation state regulated at excitation step S1, that is, the b-side of the exciting coil 1a2 becomes a non-excited state and the exciting coil 1a2 becomes the S pole, the N pole of the rotor 1b is attracted toward the a-side of the exciting coil 1a1, and the rotor 1b becomes stable.
Next, excitation step S8 is reached. When the b-side of the exciting coil 1a2 becomes the N pole and the a-side of the exciting coil 1a1 becomes the S pole, the rotor 1b turns by 9 degrees in an arrow Y1 direction from the position of excitation step S1 and stops, whereby the pointer 2 shifts in an arrow Y3 direction (FIG. 5).
Following the above, when the b-side of the exciting coil 1a2 and the a-side of the exciting coil 1a1 are respectively controlled as follows:
N pole, non-excited state (excitation step S7)xe2x86x92
N pole, N pole (excitation step S6)xe2x86x92
non-excited state, N pole (excitation step S5)xe2x86x92
S pole, N pole (excitation step S4)xe2x86x92
S pole, non-excited state (excitation step S3)xe2x86x92
S pole, S pole (excitation step S2), the rotor 1b turns by 9 degrees each time following the change of the excitation state.
When the excitation state of excitation step S8 is generated again from excitation step S1, the rotor 1b rotates again by 9 degrees in the arrow Y1 direction and becomes stable. Like the above, the rotor 1b turns by 9 degrees every step in the arrow Y1 direction by repeatedly controlling the excitation state of the exciting coils 1a1, 1a2 according to the excitation pattern consisting of the excitation steps S8 to S1.
In order to rotate the rotor 1b in an arrow Y2 direction, the excitation state of the exciting coils 1a1, 1a2 is controlled according to a pattern opposite the above excitation pattern, i.e., from S1 toward S8, whereby the pointer 2 shifts in an arrow Y4 direction (FIG. 5).
Next, an operation of the above indicating apparatus used for a vehicle-speedometer, for example, is described hereinafter. An angle data D1 is supplied to the drive controller 4, which angle data D1 shows a rotation angle of the rotor 1b corresponding to a travel which is a difference between a target position of the pointer 2 and a present position thereof. The target position of the pointer 2 is calculated on the basis of speed information from a speed sensor. By means of the drive controller 4 controlling an excitation state of the exciting coils 1a1, 1a2 according to this angle data D1, the pointer 2 shifts by only the above travel and indicates the target position.
With respect to the above indicating apparatus, however, a power swing caused by an input of the angle data D1 affected by vibration and noise of the vehicle body could be brought about, wherein an actual travel of the pointer 2 differs from the target travel of the pointer 2. If the power swing is repeated, a difference arises between the speed indicated by the pointer 2 and the speed information from the speed sensor, whereby the indicating apparatus can not carry out an accurate indication.
In order to solve such a problem, as shown in FIG. 5, a stopper 5 is provided at a position at which the pointer 2 indicates zero (for example, 0 km/h) so as to stop the pointer 2 thereat by shifting the pointer 2 toward the stopper 5 every timing of ignition ON/OFF or battery connection. That is, a reset operation to reset the difference between the speed indicated by the pointer 2 and the speed information from the speed sensor is carried out. Hereinafter, a rotation in the arrow Y1 direction is called a reverse rotation. On the contrary, a rotation in the arrow Y2 direction is called a normal rotation.
With respect to the above prior art indicating apparatus, however, the rotor 1b has to be reversed so that the pointer 2 securely abuts the stopper 5. That is, the rotor 1b has to be reversed so that the pointer 2 can return larger than a normal deflection. Therefore, because the above reset operation has to be carried out regardless of the presence or absence of the difference between the speed indicated by the pointer 2 and the speed information from the speed sensor, much time is required for the reset operation.
Because the excitation state of the exciting coils 1a1, 1a2 is continuously controlled even though the pointer 2 has fully returned to the stopper 5, the pointer 2 repeats abutting and leaving the stopper 5, thereby making an unpleasant clattering noise.
In order to solve the above problem, the indicating apparatus which closes the reset operation simultaneously with the abutment of the pointer 2 against the stopper 5 is proposed. That is, because an induction voltage is generated in the exciting coil 1a1 or 1a2 being in a no-excited state while the pointer 2 is not in contact with the stopper 5 and therefore the rotor 1b is moving, and, on the other hand, because an induction voltage is not generated in the exciting coil being in a non-excited state while the pointer 2 is in contact with the stopper 5 and, therefore, the rotor 1b is stopping, the voltage generated in either, being in the non-excited state, of the exciting coils can be detected at a timing of the exciting coil being controlled into the non-excited state.
Whether or not the induction voltage has been generated is judged, and if yes, movement of the pointer 2 is stopped on a judgment that the pointer 2 has abutted the stopper 5.
However, the rotor 1b is not likely to stop immediately after the pointer 2 abutted the stopper 5 but to further turn by some gap of gears 3.
The rotor 1b is continuously controlled to reverse in the state that the pointer 2 is in contact with the stopper 5, the rotor 1b sometimes normally rotates at a timing of the exciting coils 1a1, 1a2 being changed to the proper excited states.
Specifically, if the pointer 2 is to abut the stopper 5, for example, in a state of the exciting coils 1a1, 1a2 being in the excitation state regulated at excitation step S2, and when the pointer 2 is abutting the stopper 5 and the rotor 1b is stopping at the position shown in excitation step S2, the rotor 1b could normally rotate near excitation step S4 if the exciting coils 1a1, 1a2 are continuously controlled according to an excitation pattern of S1xe2x86x92S8xe2x86x92S7xe2x86x92S6xe2x86x92S5xe2x86x92S4xe2x86x92S3xe2x86x92S2xe2x86x92S1 . . . .
Induction voltage is generated by the normal rotation of the rotor 1b at step S3 even though the pointer 2 has already abutted the stopper 5, and therefore it can not be detected that the pointer 2 has arrived at the predetermined. A time-period of a completely stopping state of the rotor after the abutment of the pointer 2 against the stopper 5 is the one from excitation step S8 to excitation step S5 and is a very short. The time-period of the completely stopping state of the rotor after the abutment of the pointer 2 against the stopper 5 could become shorter according to a state of magnetization of the rotor 1b and so on.
With respect to the prior art apparatus, however, because the presence of the induction voltage can be detected only at the timing of the non-excited state, detection of the abutment of the pointer 2 against the stopper 5 would be difficult.
In view of the foregoing, an object of the present invention is to provide a stepping motor which can securely detect an abutment of a driven member against a stopper and a driving apparatus which can also securely detect an abutment of a driven member against a stopper.
In order to achieve the above object, as a first aspect of the present invention, a stepping motor comprises: exciting coils; a rotor provided with a plurality of N/S poles so as to rotate following a change of an excitation state of the exciting coils; and a detecting coil provided separately from the exciting coils so as to generate induction voltage according to rotation of the rotor.
According to the present invention with the first aspect, because the detecting coil is provided in addition to the exciting coils, the presence or absence of induction voltage generated in the detecting coil can be detected at each excitation step. Therefore, because whether or not the rotor is turning or stopping can be judged, the abutment of the driven member against the stopper can be securely detected.
As a second aspect of the present invention, based on the first aspect, the exciting coils are provided along a peripheral surface of the rotor, and the detecting coil is provided at a center of a longest peripheral surface between adjoining exciting coils.
According to the present invention with the second aspect, because the detecting coil is provided at a center of a longest peripheral surface between adjoining exciting coils, the detecting coil can be prevented from receiving an influence from the excitation state of the exciting coils, thereby further securely ensuring detection of the abutment of the driven member against the stopper.
As a third aspect of the present invention, a driving apparatus comprises: a stepping motor having: exciting coils, a rotor provided with a plurality of N/S poles so as to rotate following a change of an excitation state of the exciting coils, and a detecting coil provided separately from the exciting coils so as to generate induction voltage according to rotation of the rotor; a driven member linked with the rotor; a stopper to mechanically stop the driven member at a predetermined position; a first exciting means to normally or reversely rotate the rotor by controlling the excitation state of the exciting coils; a second exciting means to reverse the rotor in a direction of making the driven member move toward the predetermined position by controlling the excitation state of the exciting coils; a position detecting means to detect the driven member having abutted the stopper and stopped at the predetermined position on a basis of induction voltage generated in the detecting coil during control by the second exciting means; and a controlling means which stops the first exciting means controlling and starts the second exciting means controlling when an instruction signal is inputted, and which starts the first exciting means controlling and stops the second exciting means controlling when the position detecting means detects the driven member having stopped at the predetermined position.
According to the present invention with the third aspect, in the stepping motor, the rotor provided with a plurality of N/S poles rotates following a change of an excitation state of the exciting coils, and the detecting coil provided separately from the exciting coils generates an induction voltage according to rotating of the rotor. The stopper mechanically stops the driven member at a predetermined position. In addition, the first exciting means normally or reversely rotates the rotor by controlling the excitation state of the exciting coils. Further, the second exciting means reverses the rotor in a direction of making the driven member move toward the predetermined position by controlling the excitation state of the exciting coils.
The position detecting means detects the driven member having abutted the stopper and stopped at the predetermined position on a basis of induction voltage generated in the detecting coil during control by the second exciting means. The controlling means stops the first exciting means controlling and starts the second exciting means controlling when an instruction signal is inputted, and also starts the first exciting means controlling and stops the second exciting means controlling when the position detecting means detects the driven member having stopped at the predetermined position.
Therefore, because the detecting coil is provided in addition to the exciting coils, the presence or absence of an induction voltage generated in the detecting coil can be detected at each excitation stop. Therefore, because whether or not the rotor is turning or stopping can be judged, the abutment of the driven member against the stopper can be securely detected in the driving apparatus.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.